Calcifying epithelial odontogenic tumor showing microscopic features of potential malignant behavior

Calcifying epithelial odontogenic tumor (CEOT) is a rare benign, but locally aggressive, odontogenic tumor, and only 2 cases of malignant CEOT are reported in the literature. We describe a case of an atypical CEOT that penetrates the blood vessels, invades bone, and perforates the cortical plates of the mandible. On histologic examination, it shows marked pleomorphism and numerous mitotic figures, including a tripolar mitotic figure. Proliferating activity was found to be 5 times higher than typical CEOTs as demonstrated by the proliferating index, Ki-67, and analyzed by a computerized image analysis system. The Ki-67 labeling index of this case was also compared to various previously reported benign and malignant neoplasms. Although there is no clinical finding of metastasis, we believe this neoplasm has malignant potential on the basis of the histologic features of vascular invasion, significant mitotic activity, atypical mitotic figures, and an increased proliferating index.